The present invention relates to apparatus which protects integrated circuits from damage due to exposure to transient voltages of considerably higher levels than their normal operating voltages.
Overvoltage transients can and frequency do damage IC (integrated circuit) devices. Such IC devices are often housed in thin rectangular molded plastic containers having two rows of seven or more vertical leads, called dual in-line (DIP) packages. The leads may be inserted into holes in a printed circuit board and soldered to the underlying wire traces of the board. Quite often, however, the leads of a dual in-line IC package are instead plugged into a matching dual in-line socket which in turn has its leads soldered to the printed circuit board of an electronic system. In this manner, the IC device can be quickly and easily installed or removed from the system.
The present technology for protecting such IC devices from damage caused by high voltage transients involves the use of shielding, filters, and voltage clamping components such as either metal oxide varistors (MOV's) or Zener diodes installed directly onto the printed circuit boards of the electronic system. Because of cost factors and space limitations however, discrete MOV devices and Zener diodes are normally used to protect only the most critical components of the electronic system, leaving the remaining components unprotected and therefore subject to damage from such transients.
Metal oxide varistors are two terminal non-linear devices used to clamp a circuit node at a specified maximum voltage. They have the capability of shunting substantially more energy than Zener diodes, and are therefore a more suitable device for providing electrical transient protection. Until recently however, MOV devices having sufficiently low clamping threshold voltages for protecting low operating voltage components, such as IC devices, were not readily available. Typical IC devices may have operating voltages in the order of five volts, and may be damaged when subjected to transient or sustained potentials in excess of thirty volts. Now it is possible to manufacture MOV devices having clamping voltages of 8.2 volts or 12 volts, for example, making MOV devices very attractive devices for the protection of IC devices from overvoltage transients.